The Depth-Width Correlation for Shrinkage-Induced Cracks and Its Influence on Chloride Diffusion into Concrete.

This study examined the depth-width correlation of actual shrinkage-induced cracks and its influence on the diffusion properties of concrete. An experimental setup of restrained slabs was utilized to induce the shrinkage cracks, and the geometry characteristics were quantified with image analysis technology. The results indicated the depth-width scaling λ of shrinkage cracks increases with crack width and was almost constant when the crack width was approximately 0.3 mm or more, and the tip angle of shrinkage cracks is about 1-2 degrees. The diffusion coefficients of concretes were measured by a conductivity test method. A series-parallel composite model with λ was devised to evaluate the diffusivity of shrinking cracked concrete. It was shown that the equivalent diffusion coefficient depended greatly on the crack depth instead of the crack width, and it was found to be a nonlinear relationship versus the width combining with λ. The diffusion coefficient of the crack Dcr was correlated to both crack width and λ, and increased with crack width. When the crack width is higher than 0.2 mm Dcr becomes constant, where the value obtained was 87% of the diffusion coefficient in free solution.